The chairman of the House Intelligence Committee announced Thursday that he is stepping aside from the investigation of Russian interference in the 2016 presidential election until he can clear himself of "baseless" ethics complaints filed against him by "left-wing activist groups."

Rep. Devin Nunes, California Republican, said ethics charges that have been filed against him are "entirely false and politically motivated," but said the committee is better off not having to deal with the added distraction.

"I believe it is in the best interests of the House Intelligence Committee and the Congress for me to have Representative Mike Conaway, with assistance from Representatives Trey Gowdy and Tom Rooney, temporarily take charge of the Committee's Russia investigation while the House Ethics Committee looks into this matter," Mr. Nunes said in a statement.

"I will continue to fulfill all my other responsibilities as Committee Chairman, and I am requesting to speak to the Ethics Committee at the earliest possible opportunity in order to expedite the dismissal of these false claims," he said.

Mr. Nunes has faced a barrage of criticism over the way he has handled the Russian probe.

Democrats have called on him to recuse himself from the probe, questioning whether he is too close the President Trump to carry out the investigation of allegations of collusion between Russian officials and the Trump campaign.

The chairwoman and ranking member of the Committee on Ethics said Thursday saying they are looking into allegations of "unauthorized disclosures of classified information" that have been leveled against Mr. Nunes.

"The Committee notes that the mere fact that it is investigating these allegations, and publicly disclosing its review, does not itself indicate that any violation has occurred, or reflect any judgement on behalf of the Committee," Reps. Susan W. Brooks, Indiana Republican, and Theodore E. Deutch, Florida Democrat, said in a joint statement.

A White House spokesman refused to take sides, saying, "This is an internal matter for the House."

Rep. Adam Schiff, the ranking member on the House Intelligence Committee, said Mr. Nunes made the correct move.

"I know this was not an easy decision for the Chairman, with whom I have worked well for many years," said Mr. Schiff, California Democrat. "He did so in the best interests of the committee and I respect that decision.

"I look forward to my continued work with the Chairman on the whole host of other important issues that our committee oversees every day, in our effort to make sure that the country is protected and our civil liberties are maintained," Mr. Schiff said.

House Speaker Paul Ryan, meanwhile, said that Mr. Nunes made the right move and retains his trust.

"I know he is eager to demonstrate to the Ethics Committee that he has followed all proper guidelines and laws," Mr. Ryan said. "In the meantime, it is clear that this process would be a distraction for the House Intelligence Committee's investigation into Russian interference in our election.

"I am confident that he will oversee a professional investigation into Russia's actions and follow the facts wherever they lead," the Wisconsin Republican said.

House Minority Leader Nancy Pelosi, California Democrat, said she hopes the committee can move forward with a fair investigation now that Mr. Nunes has handed over the reins to Mr. Conaway of Texas, Mr. Gowdy of South Carolina and Mr. Rooney of Florida.

"I did have plenty reason that [Mr. Nunes] should not be in that role," Mrs. Pelosi told reporters on Capitol Hill. "Both because of his role in the Trump transition, and because of his erratic, bizarre, behavior as chairman of the committee."

The barrage of criticism Mr. Nunes faced centers around a March 20 meeting he had at the White House. After the gathering, Mr. Nunes hastily held a press conference outside on the lawn to announce that he had just viewed raw intelligence reports showing Mr. Trump and his associates had been swept up in U.S. surveillance of foreign targets and "unmasked."

According to regulations governing international and domestic surveillance of foreign targets, the names of Americans incidentally collected are required to be blacked out, or "masked," when the information is later compiled in a report for privacy purposes. Mr. Nunes said he'd seen Trump campaign names unmasked.

Mr. Nunes served on the Trump transition team, and the accusation of unmasking caused his Democratic counterparts on the committee, including Mr. Schiff, and some leading Republicans senators to question his impartiality. Mr. Schiff called for him to recuse himself from the House panel's investigation into Russian election meddling.

On Monday, the firestorm around Mr. Nunes's unmasking spread to the former Obama administration's national security adviser Susan E. Rice, when reports emerged that she played a central role in the "unmasking" during the final months of the Obama administration.

Ms. Rice on Tuesday categorically denied that she did anything wrong by "unmasking" the identities but did not explicitly deny having requested that names be added to raw surveillance intelligence relating to Trump associates.

But she pushed back hard against insinuations that her actions were politically motivated or tied to any organized scheme to compile dirt on the Trump campaign.

The revelation has added a fresh twist to an increasingly heated debate in Washington over the extent to which the Obama administration's handling of classified information should become the focus of congressional probes of Russian meddling in last year's election.